Nonaqueous electrolyte, lithium-ion battery, battery module, battery pack, and apparatus

ABSTRACT

This application provides a nonaqueous electrolyte, a lithium-ion battery, a battery module, a battery pack, and an apparatus. The nonaqueous solvent includes a nonaqueous solvent and a lithium slat. The nonaqueous solvent includes a carbonate solvent and a high oxidation potential solvent, and the high oxidation potential solvent is selected from one or more of compounds represented by formula I and formula II. Based on a total weight of the nonaqueous solvent, a weight percentage of the high oxidation potential solvent is 10% to 60%. This application can not only improve electrochemical performance of the lithium-ion battery under high temperature and high voltage and improve safety performance such as overcharge safety and hot box safety of the lithium-ion battery, but also ensure that the lithium-ion battery has some kinetic performance.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of PCT Patent Application No. PCT/CN2019/108606, entitled “NONAQUEOUS ELECTROLYTE, LITHIUM-ION BATTERY, BATTERY MODULE, BATTERY PACK, AND APPARATUS” filed on Sep. 27, 2019, which claims priority to Chinese Patent Application No. 201811140347.0, filed on Sep. 28, 2018 and entitled “NONAQUEOUS ELECTROLYTE AND LITHIUM-ION BATTERY”, both of which are incorporated herein by reference in their entirety.

TECHNICAL FIELD

This application relates to the field of batteries, and in particular, to a nonaqueous electrolyte, a lithium-ion battery, a battery module, a battery pack, and an apparatus.

BACKGROUND

Lithium-ion batteries are widely applied to electromobiles and consumer electronic products due to their advantages such as high energy density, high output power, long cycle life, and low environmental pollution. Current requirements for lithium-ion batteries are high voltage, high power, long cycle life, long storage life, and superb safety performance.

At present, nonaqueous electrolyte systems that use lithium hexafluorophosphate as a conductive lithium salt and cyclic carbonate and/or linear carbonate as a solvent are widely applied in lithium-ion batteries. However, the above nonaqueous electrolytes still have many shortcomings. For example, in a high-voltage system, cycle performance, storage performance and safety performance of the above nonaqueous electrolytes need to be improved. For another example, in a lithium cobalt oxide or high nickel ternary system, safety performance such as overcharge safety and hot box safety of lithium-ion batteries needs to be improved.

SUMMARY

In view of the problems in the Background, this application is intended to provide a nonaqueous electrolyte, a lithium-ion battery, a battery module, a battery pack and an apparatus. The nonaqueous electrolyte can not only improve electrochemical performance of a lithium-ion battery under high temperature and high voltage and improve safety performance such as overcharge safety and hot box safety of a lithium-ion battery, but also ensure that the lithium-ion battery has some kinetic performance.

In order to achieve the above objective, in a first aspect of this application, this application provides a nonaqueous electrolyte, including a nonaqueous solvent and a lithium salt. The nonaqueous solvent includes a carbonate solvent and a high oxidation potential solvent. Based on a total weight of the nonaqueous solvent, a weight percentage of the high oxidation potential solvent is 10% to 60%.

The high oxidation potential solvent is selected from one or more of compounds represented by formula I and formula II. In formula I, R¹ and R₂ are independently selected from unsubstituted, partially halogenated or fully halogenated alkyl groups having 1 to 5 carbon atoms, and at least one of R₁ and R₂ is a partially halogenated or fully halogenated alkyl group having 1 to 5 carbon atoms. In formula II, R₃ is selected from partially halogenated or fully halogenated alkylidene groups having 1 to 6 carbon atoms. A halogen atom is selected from one or more of F, Cl, Br, and I.

According to a second aspect of this application, this application provides a lithium-ion battery, including a positive electrode plate, a negative electrode plate, a separator and the electrolyte according to the first aspect of this application.

According to a third aspect of this application, this application provides a battery module, including the lithium-ion battery according to the second aspect of this application.

According to a fourth aspect of this application, this application provides a battery pack, including the battery module according to the third aspect of this application.

According to a fifth aspect of this application, this application provides an apparatus, including the lithium-ion battery according to the second aspect of this application, where the lithium-ion battery is used as a power source of the apparatus.

Compared with the prior art, this application includes at least the following beneficial effects:

(1) The nonaqueous electrolyte in this application can combine advantages of high oxidation resistance and non-flammability of high oxidation potential solvents with an advantage of low viscosity of carbonate solvents. As such, the nonaqueous electrolyte can not only improve electrochemical performance of a lithium-ion battery under high temperature and high voltage, but also ensure that the lithium-ion battery has some kinetic performance.

(2) As the nonaqueous electrolyte in this application uses a mixed solvent formed by a high oxidation potential solvent and a carbonate solvent, the nonaqueous electrolyte can overcome disadvantages of conventional carbonate solvents, such as poor oxidation resistance, easy high-pressure decomposition and gas generation, a low flash point, and easy combustion, and can also greatly improve safety performance such as overcharge safety and hot box safety of a lithium-ion battery.

The battery module, the battery pack, and the apparatus in this application include the lithium-ion battery, and therefore have at least the same advantages as the lithium-ion battery.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view of an embodiment of a lithium-ion battery;

FIG. 2 is an exploded view of FIG. 1;

FIG. 3 is a schematic diagram of an embodiment of an electrode assembly of the lithium-ion battery in FIG. 2, in which a first electrode plate, a second electrode plate, and a separator are wound to form a wound electrode assembly;

FIG. 4 is a schematic diagram of another embodiment of an electrode assembly of the lithium-ion battery in FIG. 2, in which a first electrode plate, a second electrode plate, and a separator are laminated along a thickness direction to form a laminated electrode assembly;

FIG. 5 is a perspective view of an embodiment of a battery module;

FIG. 6 is a perspective view of an embodiment of a battery pack;

FIG. 7 is an exploded view of FIG. 6; and

FIG. 8 is a schematic diagram of an embodiment of an apparatus using a lithium-ion battery as a power source.

Reference signs are described as follows:

-   1. battery pack;     -   2. upper box body;     -   3. lower box body;     -   4. battery module;         -   5. lithium-ion battery;             -   51. housing;             -   52. electrode assembly;                 -   521. first electrode plate;                 -    521 a. first current collector;                 -    521 b. first active material layer;                 -   522. second electrode plate;                 -    522 a. second current collector;                 -    522 b. second active material layer;                 -   523. separator;                 -   524. first tab;                 -   525. second tab; and             -   53. top cover assembly.

DESCRIPTION OF EMBODIMENTS

The following describes in detail a nonaqueous electrolyte, a lithium-ion battery, a battery module, a battery pack, and an apparatus according to this application.

Firstly, a nonaqueous electrolyte according to a first aspect of this application is described. The nonaqueous electrolyte includes a nonaqueous solvent and a lithium salt, where the nonaqueous solvent includes a carbonate solvent and a high oxidation potential solvent. Based on a total weight of the nonaqueous solvent, a weight percentage of the high oxidation potential solvent is 10% to 60%.

The high oxidation potential solvent is selected from one or more of compounds represented by formula I and formula II. In formula I, R₁ and R₂ are independently selected from unsubstituted, partially halogenated or fully halogenated alkyl groups having 1 to 5 carbon atoms, and at least one of R₁ and R₂ is a partially halogenated or fully halogenated alkyl group having 1 to 5 carbon atoms. In formula II, R₃ is selected from partially halogenated or fully halogenated alkylidene groups having 1 to 6 carbon atoms. A halogen atom is selected from one or more of F, Cl, Br, and I, and further, the halogen atom is F.

In formula I and formula II, the alkyl and alkylidene substituents may be straight-chained or branched. When the alkyl group or the alkylidene group is partially or fully halogenated, the halogen atom may be of one or more types.

At present, carbonate solvents are generally used in electrolytes of lithium-ion batteries. As this type of solvent has poor oxidation resistance, the solvent may have slight oxidation at even about 4V under room temperature (25° C.). As the voltage and temperature increase, the solvent has more and more substantial oxidization and gas generation. In addition, as this type of solvent has a low flash point (generally below 35° C.), the solvent may easily burn when exposed to an open flame, and releases a large amount of heat. Therefore, lithium-ion batteries using conventional carbonate solvents have high potential hazards in safety performance.

In the nonaqueous electrolyte of this application, a high oxidation potential solvent and a carbonate solvent are used to form a mixed solvent. As the high oxidation potential solvent has advantages of high oxidation resistance and non-flammability, and can overcome disadvantages of poor oxidation resistance, easy high-pressure decomposition and gas generation, a low flash point, easy combustion and the like of conventional carbonate solvents, the nonaqueous electrolyte of this application may greatly improve safety performance such as overcharge safety and hot box safety of a lithium-ion battery, and may also improve electrochemical performance such as storage life and cycle life of a high-temperature and high-voltage battery system.

In the nonaqueous electrolyte of this application, based on a total weight of the nonaqueous solvent, a weight percentage of the high oxidation potential solvent is 10% to 60%. If the weight percentage of the high oxidation potential solvent is less than 10%, the effect in overcoming the disadvantages of carbonate solvents such as poor oxidation resistance, easy high-pressure decomposition and gas generation, a low flash point, and easy combustion is not obvious. If the weight percentage of the high oxidation potential solvent is greater than 60%, overall viscosity of the nonaqueous electrolyte increases greatly, which has greater impact on kinetic performance of the lithium-ion battery. When the weight percentage of the high oxidation potential solvent is 10% to 60%, the advantages of high oxidation resistance and non-flammability of the high oxidation potential solvent may be better combined with the advantages of low viscosity of carbonate solvents. Therefore, not only electrochemical performance of the lithium-ion battery under high temperature and high voltage may be improved, but also the lithium-ion battery may be ensured to have some kinetic performance.

In the nonaqueous electrolyte of this application, as 10% to 60% of the nonaqueous solvent is the high oxidation potential solvent, an amount of carbonate solvents used is reduced, and the oxidation resistance of the nonaqueous electrolyte is improved. The disadvantages of poor oxidation resistance, easy high-pressure decomposition and gas generation, and easy combustion of conventional carbonate solvents are alleviated. As such, the safety performance such as hot box safety and overcharge safety of the lithium-ion battery may be improved. Especially in a battery system with strong positive electrode oxidation or high positive electrode oxidation potential, the nonaqueous electrolyte of this application may significantly improve safety performance such as hot box safety and overcharge safety of the lithium-ion battery. In some embodiments, based on a total weight of the nonaqueous solvent, a weight percentage of the high oxidation potential solvent is 20% to 40%.

In the nonaqueous electrolyte of this application, in some embodiments, the nonaqueous solvent includes only the carbonate solvent and the high oxidation potential solvent.

In the nonaqueous electrolyte of this application, in some embodiments, the high oxidation potential solvent contains at least one F atom, and presence of the F atom may better improve the oxidation resistance and flame retardancy of the high oxidation potential solvent.

In the nonaqueous electrolyte of this application, in some embodiments, in formula I, R₁ and R₂ are independently selected from unsubstituted, partially fluorinated or fully fluorinated alkyl groups having 1 to 5 carbon atoms, and at least one of R₁ and R₂ is a partially fluorinated or fully fluorinated alkyl group having 1 to 5 carbon atoms. Further, R₁ and R₂ are independently selected from —CH₃, —CF₃, —CH₂CH₃, —CF₂CH₃, —CH₂CF₃, —CF₂CF₃, —CH₂CH₂CH₃, —CF₂CH₂CH₃, —CH₂CH₂CF₃, —CH₂CF₂CF₃, —CF₂CH₂CF₃, —CF₂CF₂CH₃, and —CF₂CF₂CF₃, and at least one of R₁ and R₂ is —CF₃, —CF₂CH₃, —CH₂CF₃, —CF₂CF₃, —CF₂CH₂CH₃, —CH₂CH₂CF₃, —CH₂CF₂CF₃, —CF₂CH₂CF₃, —CF₂CF₂CH₃, or —CF₂CF₂CF₃.

In the nonaqueous electrolyte of this application, in some embodiments, in formula II, R₃ is selected from partially fluorinated or fully fluorinated alkylidene groups having 1 to 6 carbon atoms. Further, R₃ is selected from —CHFCH₂CH₂CH₂—, —CF₂CH₂CH₂CH₂—, —CF₂CH₂CH₂CHF—, —CF₂CH₂CH₂CF₂—, —CH₂CH₂CHFCH₂—, —CH₂CHFCHFCH₂—, —CH₂CH₂CH(CF₃)CH₂—, —CF₂CH₂CH₂CH₂CH₂—, —CF₂CH₂CH₂CH₂CF₂—, —CH₂CH₂CH₂CHFCH₂—, —CH₂CHFCH₂CHFCH₂—, —CH₂CHFCH₂CHFCHF—, —CH₂CH₂CH₂CH₂CHF—, —CH₂CH₂CH₂CH(CF₃)CH₂—, —CF₂CH₂CH₂CH₂CH₂CH₂—, —CH₂CH₂CH₂CH₂CHFCH₂—, —CH₂CHFCH₂CH₂CHFCH₂—, —CF₂CH₂CH₂CH₂CH₂CF₂—, —CH₂CH₂CH(CH₃)CH₂CHFCH₂—, and —CH₂CH₂CH(CF₃)CH₂CHFCH₂—.

In the nonaqueous electrolyte of this application, when the substituents R₁ and R₂ have a large number of carbon atoms and a large molecular weight, the high oxidation potential solvent normally has high viscosity, and the nonaqueous electrolyte may have reduced overall electrical conductivity. This will affect the effect in improving electrochemical performance such as kinetic performance and cycle life of the lithium-ion battery. In some embodiments, R₁ and R₂ are independently selected from unsubstituted, partially halogenated or fully halogenated alkyl groups having 1 to 3 carbon atoms, and at least one of R₁ and R₂ is a partially halogenated or fully halogenated alkyl group having 1 to 3 carbon atoms. Further, R₁ and R₂ are independently selected from unsubstituted, partially fluorinated or fully fluorinated alkyl groups having 1 to 3 carbon atoms, and at least one of R₁ and R₂ is a partially fluorinated or fully fluorinated alkyl group having 1 to 3 carbon atoms.

In the nonaqueous electrolyte of this application, when the substituent R₃ has a large number of carbon atoms and a large molecular weight, the high oxidation potential solvent normally has high viscosity, and the nonaqueous electrolyte may have reduced overall electrical conductivity. This will affect the effect in improving electrochemical performance such as kinetic performance and cycle life of the lithium-ion battery. In some embodiments, R₃ is selected from partially halogenated or fully halogenated alkylidene groups having 1 to 4 carbon atoms. Further, R₃ is selected from partially fluorinated or fully fluorinated alkylidene groups having 1 to 4 carbon atoms.

In the nonaqueous electrolyte of this application, in some embodiments, the high oxidation potential solvent may be specifically selected from one or more of the following compounds:

In the nonaqueous electrolyte of this application, the high oxidation potential solvent is selected from one or more of the compounds represented by formula I and formula II. By performing comparison between the two, the compound represented by formula I is characterized by lower viscosity and a lower dielectric constant, while the compound represented by formula II is characterized by higher viscosity and a higher dielectric constant. Therefore, in some embodiments, the high oxidation potential solvent includes both the compound represented by formula I and the compound represented by formula II. Further, the high oxidation potential solvent may only include the compound represented by formula I.

In the nonaqueous electrolyte of this application, in some embodiments, a weight of the compound represented by formula I accounts for 30% to 100% of a total weight of the high oxidation potential solvent, and a weight of the compound represented by formula II accounts for 0% to 70% of the total weight of the high oxidation potential solvent.

In the nonaqueous electrolyte of this application, in some embodiments, the carbonate solvent may be selected from one or more of cyclic carbonate and linear carbonate. Further, the carbonate solvent is a mixture of cyclic carbonate and linear carbonate. The linear carbonate is characterized by low viscosity, and a defect of high viscosity of the high oxidation potential solvent may be effectively alleviated by adding the linear carbonate. The cyclic carbonate has an advantage of a high dielectric constant compared with the high oxidation potential solvent. After the cyclic carbonate is added, solubility of the nonaqueous solvent to a lithium salt may be improved, which may effectively improve electrical conductivity of the nonaqueous electrolyte and contribute to obtaining a lithium-ion battery with good kinetic performance.

In the nonaqueous electrolyte of this application, in some embodiments, a weight ratio of the linear carbonate to the cyclic carbonate is 80:1 to 1:1. Further, the weight ratio of the linear carbonate to the cyclic carbonate is 15:1 to 3:1.

The cyclic carbonate may be selected from one or more of compounds represented by formula III, and the linear carbonate may be selected from one or more of compounds represented by formula IV. In formula III, R₁₁ is selected from unsubstituted alkyl groups having 1 to 5 carbon atoms. In formula IV, R₁₂ and R₁₃ are selected from unsubstituted alkyl groups having 1 to 5 carbon atoms, and R₁₂ and R₁₃ may be the same, or may be different. In formula III and formula IV, an alkyl substituent may have a straight-chained structure or a branched structure.

In some embodiments, the cyclic carbonate may be specifically selected from one or more of ethylene carbonate and propylene carbonate, and the linear carbonate may be specifically selected from one or more of ethyl methyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, methyl butyl carbonate, ethylene propyl carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate and dibutyl carbonate.

In the nonaqueous electrolyte of this application, in order to better alleviate the disadvantage that the nonaqueous electrolyte is prone to decompose and generate gas under high pressure. In some embodiments, the carbonate solvent includes at least one of ethyl methyl carbonate, dimethyl carbonate, and diethyl carbonate.

In the nonaqueous electrolyte of this application, as viscosity of the high oxidation potential solvent is typically larger than that of the carbonate solvent, electrical conductivity of the nonaqueous electrolyte may be easily affected, thereby affecting charge and discharge capacity, cycle life, and kinetic performance of the lithium-ion battery. Therefore, electrical conductivity of the nonaqueous electrolyte may be improved by using the high oxidation potential solvent in combination with a suitable type of carbonate solvent to further improve charge and discharge capacity, cycle life, and kinetic performance of the lithium-ion battery. In some embodiments, room-temperature electrical conductivity of the nonaqueous electrolyte is controlled to be greater than or equal to 5.0 mS/cm. Among carbonate solvents, linear carbonate is generally characterized by low viscosity. As such, in some embodiments, the carbonate solvent includes at least a linear carbonate. Further, the carbonate solvent includes at least one of ethyl methyl carbonate, dimethyl carbonate, and diethyl carbonate. The linear carbonate has even lower viscosity, and therefore may effectively make up for high viscosity of the high oxidation potential solvent.

In the nonaqueous electrolyte of this application, a specific type of the lithium salt is not specifically limited. The lithium salt may be any lithium salt used in existing batteries. For example, the lithium salt may be specifically selected from one or more of LiPF₆, LiN(CF₃SO₂)₂, LiN(FSO₂)₂ (LiFSI), LiBF₄, LiCF₃SO₃, and LiClO₄.

In order to further improve kinetic performance of the lithium-ion battery, in some embodiments, the lithium salt is a mixed lithium salt of LiPF₆ and LiN(FSO₂)₂. With advantages of moderate viscosity and a high degree of dissociation, LiN(FSO₂)₂ can promote ion conduction to improve electrical conductivity of the nonaqueous electrolyte, helping to obtain a lithium-ion battery with good kinetic performance. In addition, with high thermal stability, LiN(FSO₂)₂ can also improve safety performance such as overcharge safety and hot box safety of the lithium-ion battery.

In the mixed lithium salt formed by LiPF₆ and LiN(FSO₂)₂, when relative content of LiN(FSO₂)₂ is higher, electrical conductivity of the nonaqueous electrolyte is significantly improved, and kinetic performance of the lithium-ion battery is significantly improved, but a risk of corrosion to a current collector (such as aluminum foil) also increases, which is detrimental to cycle performance of the lithium-ion battery. When relative content of LiPF₆ is higher, the effect made by LiN(FSO₂)₂ in improving kinetic performance and safety performance of the lithium-ion battery is limited. In some embodiments, a weight ratio of LiPF₆ to LiN(FSO₂)₂ is 10:1 to 1:10. Further, the weight ratio of LiPF₆ to LiN(FSO₂)₂ is 4:1 to 1:4.

In the nonaqueous electrolyte of this application, specific concentration of the lithium salt is not specifically limited either, and may be adjusted according to an actual need. For example, concentration of the lithium salt may specifically be 0.7 mol/L to 2 mol/L.

In the nonaqueous electrolyte of this application, in some embodiments, the nonaqueous electrolyte may further include a film-forming additive, and the film-forming additive helps to form an interface protective film of superior performance on the negative electrode and the positive electrode, thereby further improving electrochemical performance such as kinetic performance, cycle life, and storage life of the lithium-ion battery.

In some embodiments, based on the total weight of the nonaqueous electrolyte, a weight percentage of the film-forming additive is 0.01% to 10%. Further, based on the total weight of the nonaqueous electrolyte, the weight percentage of the film-forming additive is 0.1% to 5%.

In some embodiments, the film-forming additive may be specifically selected from one or more of a cyclic carbonate compound with an unsaturated bond, a halogen-substituted cyclic carbonate compound, a sulfate compound, a sulfite compound, a sultone compound, a disulfonate compound, a nitrile compound, an aromatic compound, an isocyanate compound, a phosphazene compound, a cyclic anhydride compound, a phosphite compound, a phosphate compound, a borate compound, and a carboxylate compound.

In some further embodiments, the film-forming additive may be specifically selected from one or more of 1,3-propane sultone (PS), ethylene sulfate (DTD), fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), vinylene carbonate (VC), 1,3-propene sultone (PES), adiponitrile (ADN), and succinonitrile (SN). These types of film-forming additives help to form a stable interface protective film on the negative electrode and the positive electrode, and effectively inhibit side reactions of the high oxidation potential solvent on the negative electrode and the positive electrode, thereby effectively improve electrochemical performance such as kinetic performance, cycle life, and storage life of the lithium-ion battery.

Further, the film-forming additive contains at least DTD. Although the high oxidation potential solvent has the advantages of high oxidation resistance and non-flammability, the high oxidation potential solvent has poor compatibility with the negative electrode and may have side reactions on the negative electrode. After DTD is added, a stable interface protective film may first be formed on the negative electrode, thereby suppressing side reactions of the high oxidation potential solvent on the negative electrode. In addition, DTD may generate lithium sulfate that structurally contained an alkoxy structure (—CH₂CH₂O—) during the process of film forming on the negative electrode. This can effectively adjust viscoelasticity of the interface protective film on the negative electrode, further improve kinetics of lithium ion transfer at the interface, and finally form a thin and dense interface protective film with good kinetics of lithium ion transfer on the negative electrode. In addition, DTD may also form a stable interface protective film on a surface of the positive electrode to further improve oxidation resistance of the nonaqueous electrolyte. As such, the addition of DTD may better improve kinetic performance and electrochemical performance such as cycle life and storage life of the lithium-ion battery, and may also improve safety performance such as overcharge safety and hot box safety of the lithium-ion battery to some extent.

Yet in some further embodiments, the film-forming additive contains at least both DTD and FEC. Provided that DTD is added, after FEC is further added, cycle life of the lithium-ion battery is further improved. A possible reason is that: FEC may be reduced on the negative electrode to form a stable interface protective film, thereby weakening reduction reactions of DTD on the negative electrode. This may help to improve film forming quality of DTD on a surface of the positive electrode, which further facilitates improvement of cycle life of the lithium-ion battery.

Next, a lithium-ion battery according to a second aspect of this application is described.

FIG. 1 is a perspective view of an embodiment of a lithium-ion battery 5. FIG. 2 is an exploded view of FIG. 1. FIG. 3 is a schematic diagram of an embodiment of an electrode assembly 52 of the lithium-ion battery 5 in FIG. 2, in which a first electrode plate 521, a second electrode plate 522, and a separator 523 are wound to form a wound electrode assembly. FIG. 4 is a schematic diagram of another embodiment of an electrode assembly 52 of the lithium-ion battery 5 in FIG. 2, in which a first electrode plate 521, a second electrode plate 522, and a separator 523 are laminated along a thickness direction to form a laminated electrode assembly.

With reference to FIG. 1 to FIG. 4, the lithium-ion battery 5 includes a housing 51, the electrode assembly 52, a top cover assembly 53, and an electrolyte (not shown).

The electrode assembly 52 is accommodated in the housing 51. The electrode assembly 52 includes the first electrode plate 521, the second electrode plate 522, the separator 523, a first tab 524, and a second tab 525. The separator 523 separates the first electrode plate 521 from the second electrode plate 522.

The first electrode plate 521 includes a first current collector 521 a and a first active material layer 521 b provided on a surface of the first current collector 521 a. The first active material layer 521 b contains a first active material. The first active material layer 521 b may be provided on one surface or two surfaces of the first current collector 521 a depending on an actual need. The second electrode plate 522 includes a second current collector 522 a and a second active material layer 522 b provided on a surface of the second current collector 522 a. The second active material layer 522 b may be provided on one surface or two surfaces of the second current collector 522 a depending on an actual need. The second active material layer 522 b contains a second active material. The first active material and the second active material implement deintercalation of lithium ions. Electrical polarities of the first electrode plate 521 and the second electrode plate 522 are opposite. To be specific, one of the first electrode plate 521 and the second electrode plate 522 is a positive electrode plate, and the other of the first electrode plate 521 and the second electrode plate 522 is a negative electrode plate. The first tab 524 may be formed by cutting the first current collector 521 a, or may be formed separately and fixedly connected to the first current collector 521 a. Similarly, the second tab 525 may be formed by cutting the second current collector 522 a, or may be formed separately and fixedly connected to the second current collector 522 a.

A quantity of the electrode assemblies 52 is not limited, and may be one or more.

The electrolyte is injected into the housing 51 and impregnates the electrode assembly 51. Specifically, the electrolyte impregnates the first electrode plate 521, the second electrode plate 522, and the separator 523.

It is noted that the lithium-ion battery 5 shown in FIG. 1 is a tank type battery, but is not limited thereto. The lithium-ion battery 5 may be a pouch type battery, which means that the housing 51 is replaced by a metal plastic film and the top cover assembly 53 is eliminated.

In the lithium-ion battery 5, as one of the first electrode plate 521 and the second electrode plate 522 is the positive electrode plate, a current collector of the positive electrode plate is a positive current collector, an active material layer of the positive electrode plate is a positive active material layer, and an active material of the positive electrode plate is a positive active material. As such, the positive electrode plate includes the positive current collector and the positive active material layer provided on a surface of the positive current collector.

In another word, the lithium-ion battery according to the second aspect of this application includes a positive electrode plate, a negative electrode plate, a separator and the nonaqueous electrolyte according to the first aspect of this application.

In the lithium-ion battery in this application, the positive electrode plate may include a positive active material, a conductive agent and a binder. The positive active material may be selected from a layered lithium-containing oxide, a spinel-type lithium-containing oxide, and the like. Specifically, the positive active material may be selected from one or more of a lithium cobalt oxide, a lithium nickel oxide, a lithium manganese oxide, a lithium nickel manganese oxide, a lithium nickel cobalt manganese oxide, and a lithium nickel cobalt aluminum oxide. However, this application is not limited to these materials, and other conventionally well-known materials that can be used as a positive active material of a lithium-ion battery may also be used. One type of these positive active materials may be used alone, or two or more types may be used in combination, at a combination ratio adjustable depending on an actual need. Types of the conductive agent and the binder are not specifically limited, and may be selected depending on an actual need.

When voltage of the lithium-ion battery is higher, the lithium-ion battery may have higher charge and discharge capacity and higher energy density, but a conventional electrolyte may be oxidized to produce gas and release heat. This may change service life and high-temperature performance of the lithium-ion battery, especially in the process of abuse. For example, at a 150° C. hot box, the lithium-ion battery may easily burn. However, the nonaqueous electrolyte of this application contains a high oxidation potential solvent, which can greatly improve oxidation resistance of the nonaqueous electrolyte and reduce heat release, thereby effectively improving high-temperature performance of the lithium-ion battery. As such, the nonaqueous electrolyte in this application can more significantly improve performance of a battery system with high positive electrode oxidation or high positive electrode oxidation potential, especially electrochemical performance of the lithium-ion battery under high temperature and high voltage. Gas generation of the lithium-ion battery under high temperature and high voltage may be even more significantly suppressed, and safety performance such as overcharge safety and hot box safety of the lithium-ion battery may also be more significantly improved.

In some embodiments, the positive active material is one or more of Li_(1+x)Ni_(a)Co_(b)M′_((1−a−b))O_(2−c)Y_(c), and Li_(1+y)Ni_(m)Mn_(n)M″_(2−m−n)O_(4−p)Z_(p), where −0.1≤x≤0.2, 0.6≤a≤1, 0≤b<1, 0≤(1-ab)<1, 0≤c<1, M′ is selected from one or more of Mn, Al, Mg, Zn, Ga, Ba, Fe, Cr, Sn, V, Sc, Ti, and Zr, and Y is selected from one or more of F, Cl, and Br; −0.1≤y≤0.2, 0.4≤m≤1.2, 0.8≤n≤1.6, 0≤(2-mn)≤0.3, 0≤p≤1, M″ is selected from one or more of Al, Mg, Zn, Ga, Ba, Fe, Cr, Sn, V, Sc, Ti, and Zr, and Z is selected from one or more of F, Cl, and Br. Further, the positive active material may be specifically selected from one or more of LiNi_(0.6)Co_(0.2)Mn_(0.2)O₂ (NCM622), LiNi_(0.8)Co_(0.1)Mn_(0.1)O₂ (NCM811), LiNi_(0.85)Co_(0.15)Al_(0.05)O₂, and LiNi_(0.5)Mn_(1.5)O₄. As Ni content in the positive active material increases, the positive active material has increased charge and discharge capacity, but reduced thermal stability. As such, the positive active material may release a strong oxidizing substance under high temperature, oxidizing the nonaqueous electrolyte and deteriorating high-temperature performance of the lithium-ion battery. The nonaqueous electrolyte of this application contains an oxidation resistant high oxidation potential solvent, which can greatly improve oxidation resistance of the nonaqueous electrolyte and reduce heat release, thereby effectively improving high-temperature performance of the lithium-ion battery

In the lithium-ion battery in this application, in some embodiments, an end-of-charge voltage of the lithium-ion battery is U, where 4.3V≤U≤6V. That is, the nonaqueous electrolyte in this application may increase the end-of-charge voltage of the lithium-ion battery to 4.3V or more.

In the lithium-ion battery in this application, the negative electrode plate may include a negative active material, a conductive agent and a binder. The negative active material may be selected from a carbon-based material, a silicon-based material, a tin-based material, and the like. Specifically, the negative active material may be selected from soft carbon, hard carbon, artificial graphite, natural graphite, silicon, silicon oxide, silicon carbon composite, silicon alloy, tin, tin oxide, tin alloy, lithium titanate, a metal that can form an alloy with lithium, and the like. However, this application is not limited to these materials, and other conventionally well-known materials that can be used as a negative active material of a lithium-ion battery may also be used. One type of these negative active materials may be used alone, or two or more types may be used in combination, at a combination ratio adjustable depending on an actual need. Types of the conductive agent and the binder are not specifically limited, and may be selected depending on an actual need.

In the lithium-ion battery of this application, a specific type of the separator is not specifically limited, and the separator may be made of any separator material used in existing batteries, such as a polyolefin separator, a ceramic separator, or the like. Specifically, the separator may be a polyethylene film, a polypropylene film, a polyvinylidene fluoride film, or a multilayer composite film thereof, but this application is not limited thereto.

A battery module according to a third aspect of this application is described next.

FIG. 5 is a perspective view of an embodiment of a battery module 4.

The battery module 4 provided in the third aspect of this application includes the lithium-ion battery 5 according to the second aspect of this application.

Referring to FIG. 5, the battery module 4 includes a plurality of lithium-ion batteries 5. The plurality of lithium-ion batteries 5 are arranged in a longitudinal direction. The battery module 4 may be used as a power source or an energy storage apparatus. A quantity of lithium-ion batteries 5 included in the battery module 4 may be adjusted based on use and capacity of the battery module 4.

A battery pack according to a fourth aspect of this application is described next.

FIG. 6 is a perspective view of an embodiment of a battery pack 1. FIG. 7 is an exploded view of FIG. 6.

The battery pack 1 provided in the fourth aspect of this application includes the battery module 4 according to the third aspect of this application.

Specifically, referring to FIG. 6 and FIG. 7, the battery pack 1 includes an upper box body 2, a lower box body 3, and the battery module 4. The upper box body 2 and the lower box body 3 are assembled together to form a space for accommodating the battery module 4. The battery module 4 is disposed in the space formed by the upper box body 2 and the lower box body 3 that are assembled together. An output electrode of the battery module 4 penetrates through one or both of the upper box body 2 and the lower box body 3 to output power or to charge from an outer source. A quantity and an arrangement of the battery modules 4 used in the battery pack 1 may be determined depending on an actual need.

An apparatus according to a fifth aspect of this application is described next.

FIG. 8 is a schematic diagram of an embodiment of an apparatus using a lithium-ion battery as a power source.

The apparatus provided in the fifth aspect of this application includes the lithium-ion battery 5 according to the second aspect of this application, where the lithium-ion battery 5 may be used as a power source for the apparatus. In FIG. 8, the apparatus using the lithium-ion battery 5 is an electric automobile. The apparatus using the lithium-ion battery 5 is obviously not limited to this, but may be any electric vehicles other than electric automobiles (for example, an electric bus, an electric tram, an electric bicycle, an electric motorcycle, an electric scooter, an electric golf cart, and an electric truck), an electric vessel, an electric tool, an electronic device, and an energy storage system. The electric automobile may be a full electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. Certainly, depending on an actual use form, the apparatus provided in the fifth aspect of this application may include the battery module 4 according to the third aspect of this application. Certainly, the apparatus provided in the fifth aspect of this application may also include the battery pack 1 according to the fourth aspect of this application.

To make the objectives, technical solutions, and beneficial technical effects of this application clearer, this application is further described below in detail with reference to embodiment examples. It should be understood that the embodiment examples described in this specification are merely intended to explain this application, but not to limit this application. Formulations, proportions, and the like in the embodiment examples may be selected as appropriate to local conditions, which has no substantial effect on results.

Example 1

(1) Preparation of a Nonaqueous Electrolyte

Ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed at a weight ratio of 30:70 to be used as a carbonate solvent, and a compound A1 was used as a high oxidation potential solvent. A weight ratio of the carbonate solvent to the high oxidation potential solvent was 40:60. After that, 1.0 mol/L LiPF₆ was dissolved as a lithium salt to prepare a nonaqueous electrolyte denoted as C1.

(2) Preparation of a Positive Electrode Plate

A positive active material LiNi_(0.8)Co_(0.1)Mn_(0.1)O₂, an acetylene black conductive agent, and a polyvinylidene fluoride (PVDF) binder were fully stirred and uniformly mixed in an N-methylpyrrolidone solvent system at a weight ratio of 94:3:3, and then the mixture was applied onto a current collector Al foil, followed by drying and cold pressing to obtain a positive electrode plate.

(3) Preparation of a Negative Electrode Plate

A negative active material artificial graphite, an acetylene black conductive agent, a styrene-butadiene rubber binder, a sodium carboxymethyl cellulose thickener were fully stirred and uniformly mixed at a weight ratio of 95:2:2:1 in a deionized water solvent system, and then the mixture was applied onto a current collector Cu foil, followed by drying and cold pressing to obtain a negative electrode plate.

(4) Preparation of a Separator

A polyethylene film was used as a separator.

(5) Preparation of a Lithium-Ion Battery

The positive electrode plate, the separator, and the negative electrode plate were laminated in order, so that the separator was interposed between the positive electrode plate and negative electrode plate to provide separation. Then the laminated product was wound to obtain an electrode assembly. The electrode assembly was placed in an outer package and dried, and the nonaqueous electrolyte was then injected. Then, after vacuum packaging, standing, chemical conversion, shaping, and other processes, a lithium-ion battery was obtained.

Example 2

A nonaqueous electrolyte and a lithium-ion battery were prepared according to the same method as in Example 1, except that a weight ratio of a carbonate solvent to a high oxidation potential solvent in a nonaqueous solvent of the nonaqueous electrolyte was 50:50. The nonaqueous electrolyte was denoted as C2.

Example 3

A nonaqueous electrolyte and a lithium-ion battery were prepared according to the same method as in Example 1, except that a weight ratio of a carbonate solvent to a high oxidation potential solvent in a nonaqueous solvent of the nonaqueous electrolyte was 60:40. The nonaqueous electrolyte was denoted as C3.

Example 4

A nonaqueous electrolyte and a lithium-ion battery were prepared according to the same method as in Example 1, except that a weight ratio of a carbonate solvent to a high oxidation potential solvent in a nonaqueous solvent of the nonaqueous electrolyte was 70:30. The nonaqueous electrolyte was denoted as C4.

Example 5

A nonaqueous electrolyte and a lithium-ion battery were prepared according to the same method as in Example 1, except that a weight ratio of a carbonate solvent to a high oxidation potential solvent in a nonaqueous solvent of the nonaqueous electrolyte was 80:20. The nonaqueous electrolyte was denoted as C5.

Example 6

A nonaqueous electrolyte and a lithium-ion battery were prepared according to the same method as in Example 1, except that a weight ratio of a carbonate solvent to a high oxidation potential solvent in a nonaqueous solvent of the nonaqueous electrolyte was 90:10. The nonaqueous electrolyte was denoted as C6.

Example 7

A nonaqueous electrolyte and a lithium-ion battery were prepared according to the same method as in Example 4, except that a weight ratio of ethylene carbonate (EC) to ethyl methyl carbonate (EMC) in the nonaqueous electrolyte was 10:90. The nonaqueous electrolyte was denoted as C7.

Example 8

A nonaqueous electrolyte and a lithium-ion battery were prepared according to the same method as in Example 4, except that a weight ratio of ethylene carbonate (EC) to ethyl methyl carbonate (EMC) in the nonaqueous electrolyte was 2:98. The nonaqueous electrolyte was denoted as C8.

Example 9

A nonaqueous electrolyte and a lithium-ion battery were prepared according to the same method as in Example 4, except that a high oxidation potential solvent in a nonaqueous solvent of the nonaqueous electrolyte was a compound A2. The nonaqueous electrolyte was denoted as C9.

Example 10

A nonaqueous electrolyte and a lithium-ion battery were prepared according to the same method as in Example 4, except that a high oxidation potential solvent in a nonaqueous solvent of the nonaqueous electrolyte was a compound A3. The nonaqueous electrolyte was denoted as C10.

Example 11

A nonaqueous electrolyte and a lithium-ion battery were prepared according to the same method as in Example 4, except that a high oxidation potential solvent in a nonaqueous solvent of the nonaqueous electrolyte was a compound A4. The nonaqueous electrolyte was denoted as C11.

Example 12

A nonaqueous electrolyte and a lithium-ion battery were prepared according to the same method as in Example 4, except that a high oxidation potential solvent in a nonaqueous solvent of the nonaqueous electrolyte was a compound A5. The nonaqueous electrolyte was denoted as C12.

Example 13

A nonaqueous electrolyte and a lithium-ion battery were prepared according to the same method as in Example 4, except that a high oxidation potential solvent in a nonaqueous solvent of the nonaqueous electrolyte was a compound A6. The nonaqueous electrolyte was denoted as C13.

Example 14

A nonaqueous electrolyte and a lithium-ion battery were prepared according to the same method as in Example 4, except that a high oxidation potential solvent in a nonaqueous solvent of the nonaqueous electrolyte was a compound A7. The nonaqueous electrolyte was denoted as C14.

Example 15

A nonaqueous electrolyte and a lithium-ion battery were prepared according to the same method as in Example 4, except that a high oxidation potential solvent in a nonaqueous solvent of the nonaqueous electrolyte was a mixture of the compound A1 and the compound A6 at a weight ratio of 70:30. The nonaqueous electrolyte was denoted as C15.

Example 16

A nonaqueous electrolyte and a lithium-ion battery were prepared according to the same method as in Example 4, except that a high oxidation potential solvent in a nonaqueous solvent of the nonaqueous electrolyte was a mixture of the compound A2 and the compound A7 at a weight ratio of 60:40. The nonaqueous electrolyte was denoted as C16.

Example 17

A nonaqueous electrolyte and a lithium-ion battery were prepared according to the same method as in Example 4, except that DTD at a weight percentage of 2% was further added into the nonaqueous electrolyte. The nonaqueous electrolyte was denoted as C17.

Example 18

A nonaqueous electrolyte and a lithium-ion battery were prepared according to the same method as in Example 4, except that PS at a weight percentage of 2% was further added into the nonaqueous electrolyte. The nonaqueous electrolyte was denoted as C18.

Example 19

A nonaqueous electrolyte and a lithium-ion battery were prepared according to the same method as in Example 4, except that VC at a weight percentage of 2% was further added into the nonaqueous electrolyte. The nonaqueous electrolyte was denoted as C19.

Example 20

A nonaqueous electrolyte and a lithium-ion battery were prepared according to the same method as in Example 4, except that FEC at a weight percentage of 2% was further added into the nonaqueous electrolyte. The nonaqueous electrolyte was denoted as C20.

Example 21

A nonaqueous electrolyte and a lithium-ion battery were prepared according to the same method as in Example 4, except that PES at a weight percentage of 2% was further added into the nonaqueous electrolyte. The nonaqueous electrolyte was denoted as C21.

Example 22

A nonaqueous electrolyte and a lithium-ion battery were prepared according to the same method as in Example 4, except that ADN at a weight percentage of 2% was further added into the nonaqueous electrolyte. The nonaqueous electrolyte was denoted as C22.

Example 23

A nonaqueous electrolyte and a lithium-ion battery were prepared according to the same method as in Example 4, except that SN at a weight percentage of 2% was further added into the nonaqueous electrolyte. The nonaqueous electrolyte was denoted as C23.

Example 24

A nonaqueous electrolyte and a lithium-ion battery were prepared according to the same method as in Example 4, except that DTD at a weight percentage of 1% and FEC at a weight percentage of 1% were further added into the nonaqueous electrolyte. The nonaqueous electrolyte was denoted as C24.

Example 25

A nonaqueous electrolyte and a lithium-ion battery were prepared according to the same method as in Example 4, except that a lithium salt in the nonaqueous electrolyte was a mixture of LiPF₆ and LiFSI at a weight ratio of 10:1, and the mixed lithium salt had a concentration of 1.1 mol/L. The nonaqueous electrolyte was denoted as C25.

Example 26

A nonaqueous electrolyte and a lithium-ion battery were prepared according to the same method as in Example 4, except that a lithium salt in the nonaqueous electrolyte was a mixture of LiPF₆ and LiFSI at a weight ratio of 1:1, and the mixed lithium salt had a concentration of 1.1 mol/L. The nonaqueous electrolyte was denoted as C26.

Comparative Example 1

A nonaqueous electrolyte and a lithium-ion battery were prepared according to the same method as in Example 1, except that no high oxidation potential solvent was contained in a nonaqueous solvent of the nonaqueous electrolyte. The nonaqueous electrolyte was denoted as D1.

Comparative Example 2

A nonaqueous electrolyte and a lithium-ion battery were prepared according to the same method as in Example 1, except that no carbonate solvent was contained in a nonaqueous solvent of the nonaqueous electrolyte. The nonaqueous electrolyte was denoted as D2.

Comparative Example 3

A nonaqueous electrolyte and a lithium-ion battery were prepared according to the same method as in Example 1, except that a weight ratio of a carbonate solvent to a high oxidation potential solvent in a nonaqueous solvent of the nonaqueous electrolyte was 95:5. The nonaqueous electrolyte was denoted as D3.

Comparative Example 4

A nonaqueous electrolyte and a lithium-ion battery were prepared according to the same method as in Example 1, except that a weight ratio of a carbonate solvent to a high oxidation potential solvent in a nonaqueous solvent of the nonaqueous electrolyte was 20:80. The nonaqueous electrolyte was denoted as D4.

Comparative Example 5

A nonaqueous electrolyte and a lithium-ion battery were prepared according to the same method as in Example 1, except that the compound A1 was replaced with methyl ethyl sulfone, and a weight ratio of a carbonate solvent to methyl ethyl sulfone was 70:30. The nonaqueous electrolyte was denoted as D5.

TABLE 1 Compositions of the nonaqueous electrolytes prepared in Examples 1 to 26 and Comparative Examples 1 to 5 Room- Composition of nonaqueous solvents and Lithium salt temperature weight percentages of individual components Con- electrical High oxidation Linear Cyclic Additive centration conductivity potential solvent carbonate carbonate Component Percentage Component mol/l mS/cm Example 1 A1  60% EMC 28% EC 12% / / LiPF₆ 1 5.7 Example 2 A1  50% EMC 35% EC 15% / / LiPF₆ 1 6.2 Example 3 A1  40% EMC 42% EC 18% / / LiPF₆ 1 6.5 Example 4 A1  30% EMC 49% EC 21% / / LiPF₆ 1 7.4 Example 5 A1  20% EMC 56% EC 24% / / LiPF₆ 1 7.7 Example 6 A1  10% EMC 63% EC 27% / / LiPF₆ 1 8.2 Example 7 A1  30% EMC 42% EC 28% / / LiPF₆ 1 8 Example 8 A1  30% EMC 35% EC 35% / / LiPF₆ 1 8.2 Example 9 A2  30% EMC 49% EC 21% / / LiPF₆ 1 7.3 Example 10 A3  30% EMC 49% EC 21% / / LiPF₆ 1 7.6 Example 11 A4  30% EMC 49% EC 21% / / LiPF₆ 1 7.5 Example 12 A5  30% EMC 49% EC 21% / / LiPF₆ 1 7.4 Example 13 A6  30% EMC 49% EC 21% / / LiPF₆ 1 6.8 Example 14 A7  30% EMC 49% EC 21% / / LiPF₆ 1 6.6 Example 15 A1:A6 = 70:30  30% EMC 49% EC 21% / / LiPF₆ 1 7.2 Example 16 A2:A7 = 60:40  30% EMC 49% EC 21% / / LiPF₆ 1 7.3 Example 17 A1  30% EMC 49% EC 21% DTD 2% LiPF₆ 1 7.3 Example 18 A1  30% EMC 49% EC 21% PS 2% LiPF₆ 1 7.2 Example 19 A1  30% EMC 49% EC 21% VC 2% LiPF₆ 1 7.3 Example 20 A1  30% EMC 49% EC 21% FEC 2% LiPF₆ 1 7.2 Example 21 A1  30% EMC 49% EC 21% PES 2% LiPF₆ 1 7.3 Example 22 A1  30% EMC 49% EC 21% ADN 2% LiPF₆ 1 7.2 Example 23 A1  30% EMC 49% EC 21% SN 2% LiPF₆ 1 7.2 Example 24 A1  30% EMC 49% EC 21% DTD + FEC 1% + 1% LiPF₆ 1 7.2 Example 25 A1  30% EMC 49% EC 21% / / LiPF₆:LiFSI = 10:1 1 7.5 Example 26 A1  30% EMC 49% EC 21% / / LiPF₆:LiFSI = 1:1 1 7.7 Comparative / / EMC 70% EC 30% / / LiPF₆ 1 8.5 Example 1 Comparative A1 100% / / / / / / LiPF₆ 1 2.6 Example 2 Comparative A1   5% EMC 67% EC 28% / / LiPF₆ 1 8.2 Example 3 Comparative A1  80% EMC 14% EC  6% / / LiPF₆ 1 3.7 Example 4 Comparative Methyl ethyl  30% EMC 49% EC 21% / / LiPF₆ 1 7.3 Example 5 sulfone

Performance tests for the lithium-ion batteries are described next.

(1) High-Temperature Storage Gas Generation Test

Five lithium-ion batteries prepared in the Examples and five lithium-ion batteries prepared in the Comparative Examples were taken and placed at room temperature, charged to 4.3V at a constant current of 0.5 C (that is, a current value at which the battery completely discharges its theoretical capacity in 2 h), and then charged at a constant voltage of 4.3V until that the current was lower than 0.05 C, such that the lithium-ion batteries were in a 4.3V fully charged state. A volume of a fully charged battery before storage was denoted as D0. The fully charged battery was placed in an oven at 85° C., taken out after 10 days, and tested for a volume after storage, where the volume after storage was denoted as D1.

A volume swelling ratio of the lithium-ion battery was ε=(D1−D0)/D0×100%.

(2) Thermal Shock Safety Performance (Hot Box) Test

Five lithium-ion batteries prepared in the Examples and five lithium-ion batteries prepared in the Comparative Examples were taken and placed at room temperature, charged to 4.3V at a constant current of 0.5 C, and then charged at a constant voltage of 4.3V until the current was lower than 0.05 C. The lithium-ion batteries were then placed in a thermostat, and the thermostat was heated to 150° C. at a heating rate of 5° C./min. Time h1 required for the thermostat to heat up from room temperature to 150° C. was recorded. The lithium-ion battery was then baked in the 150° C. thermostat until the lithium-ion battery caught smoke and a fire. Time h2 from when the thermostat was heated up from room temperature until when the lithium-ion battery caught smoke and a fire was recorded.

The thermal shock safety performance of the lithium-ion battery was characterized by time (h2−h1) for which the lithium-ion battery withstood baking at 150° C.

(3) Cycle Performance Test

Five lithium-ion batteries prepared in the Examples and five lithium-ion batteries prepared in Comparative Examples were taken, and were repeatedly charged and discharged through the following steps, and discharge capacity retention rates of the lithium-ion batteries were calculated.

First, in a room temperature environment, a first cycle of charge and discharge was performed, where the lithium-ion batteries were charged at a constant current of 0.5 C to an upper limit voltage of 4.3V, and then charged at a constant voltage of 4.3V until the current was lower than 0.05 C, and then discharged at a constant discharge current of 0.5 C until a final voltage was 3V A discharge capacity of the first cycle was recorded. 500 charge and discharge cycles were performed according to the above operations and a discharge capacity of the 500^(th) cycle was recorded.

Cycle capacity retention rate of the lithium-ion battery=(Discharge capacity at the 500^(th) cycle/Discharge capacity at the first cycle)×100%.

(4) Kinetic Performance Test

Five lithium-ion batteries prepared in the Examples and five lithium-ion batteries prepared in the Comparative Examples were taken, and then tested in a room temperature environment. First, the lithium-ion batteries were charged at a constant current of 0.5 C to an upper limit voltage of 4.3V, and then charged at a constant voltage of 4.3V until the current was lower than 0.05 C, and then discharged at a constant current with different rates (0.5 C, 2 C) until a final voltage was 3V. Discharge capacities at different rates were recorded.

The kinetic performance of the lithium-ion battery was characterized by a ratio of a discharge capacity at a rate of 2 C of the lithium-ion battery to a discharge capacity at a rate of 0.5 C of the lithium-ion battery.

TABLE 2 Performance test results of Examples 1 to 26 and the Comparative Examples 1 to 5 Hot box safety Capacity Volume performance retention swelling h2-h1 rate after ratio ε (min) cycling 2C/0.5C Example 1 13% 51 67% 54% Example 2 16% 45 72% 59% Example 3 18% 40 77% 62% Example 4 22% 36 82% 68% Example 5 24% 31 84% 73% Example 6 27% 24 88% 76% Example 7 25% 33 83% 69% Example 8 28% 31 82% 70% Example 9 21% 35 82% 69% Example 10 22% 34 83% 68% Example 11 23% 35 81% 67% Example 12 21% 35 83% 69% Example 13 18% 40 80% 58% Example 14 17% 41 79% 57% Example 15 23% 38 81% 63% Example 16 24% 37 80% 61% Example 17  8% 45 87% 79% Example 18  7% 43 85% 72% Example 19 16% 37 85% 71% Example 20 15% 35 84% 73% Example 21  5% 47 81% 64% Example 22 12% 46 72% 63% Example 23 13% 47 71% 62% Example 24  6% 47 89% 77% Example 25 20% 37 83% 70% Example 26 16% 40 84% 75% Comparative 75% 2 88% 83% Example 1 Comparative  8% 63 45% 35% Example 2 Comparative 70% 12 85% 81% Example 3 Comparative 10% 58 52% 43% Example 4 Comparative 20% 18 83% 69% Example 5

It may be seen from the test results of Comparative Examples 1 to 4 and Examples 1 to 6 that, when 10% to 60% of the nonaqueous solvent was the high oxidation potential solvent, high-temperature storage performance and hot box safety performance of the lithium-ion batteries could be significantly improved, and the lithium-ion batteries also had good cycle performance and kinetic performance. When percentage of the high oxidation potential solvent content was lower than 10% or no high oxidation potential solvent was added, because of the low content percentage, the effect in overcoming disadvantages of the carbonate solvent such as poor oxidation resistance, easy high-pressure decomposition and gas generation, a low flash point, and easy combustion was not obvious, and therefore high-temperature storage performance and hot box safety performance of the lithium-ion battery could not be effectively improved. When percentage of the high oxidation potential solvent content was higher than 60% or no carbonate solvent was added, although improvement of high-temperature storage performance and hot box safety performance of the lithium-ion battery was more obvious, deterioration of cycle performance and kinetic performance of the lithium-ion battery was also very obvious. A possible reason is that the high oxidation potential solvent added was too much, so that overall viscosity of the nonaqueous electrolyte was so high as to hinder transfer of lithium ions. In addition, as the high oxidation potential solvent added was too much, side reaction products generated on the positive and negative electrodes might also increase too much, further affecting the kinetics of lithium ion transfer.

It may be seen from the test results of Example 4 and Examples 7 and 8 that the different ratios of linear carbonate to cyclic carbonate also had some impact on performance of the lithium-ion batteries. When percentage of the cyclic carbonate content was higher, electrical conductivity of the nonaqueous electrolyte was better, and improvement of the cycle performance and kinetic performance of the lithium-ion battery was more obvious. When percentage of the linear carbonate content was higher, high-temperature stability of the nonaqueous electrolyte was better, and improvement of the high-temperature storage performance and the hot box safety performance of the lithium-ion batteries was more obvious.

It may be seen from the test results of Comparative Example 5 and Example 4 and Examples 9 to 16 that the high oxidation potential solvents that had not been fluorinated had poorer oxidation resistance and did not exhibit flame retardancy, so that the effect in improving high-temperature storage performance and hot box safety performance of the lithium-ion batteries was not desirable.

It may be also seen from the test results of Examples 9 to 16 that the high oxidation potential solvents of different structures also had some impact on performance of the lithium-ion batteries. The high oxidation potential solvent of a cyclic structure was characterized by higher viscosity and a higher dielectric constant, and the high oxidation potential solvent of a linear structure was characterized by lower viscosity and a lower dielectric constant. Therefore, in some embodiments, the high oxidation potential solvent includes both a high oxidation potential solvent of a linear structure and a high oxidation potential solvent of a cyclic structure. Further, the high oxidation potential solvent only includes a high oxidation potential solvent of a linear structure.

It may be seen from the test results of Example 4 and Examples 17 to 24 that after a film-forming additive, such as DTD, PS, VC, FEC, PES, ADN, or SN, was further added into the nonaqueous electrolyte, comprehensive performance of the lithium-ion battery had substantially been improved. A possible reason is that the film-forming additive had some film forming effect on both the positive electrode and the negative electrode, and the formed film had good stability, which inhibited continuous side reactions of the nonaqueous electrolyte during use of the battery. As such, impedance of the interface protective films on the positive electrode and negative electrode increased more slowly, and performance of the lithium-ion battery was better.

In addition, among the above film-forming additives, DTD improved performance of the lithium-ion batteries more significantly. Possible reasons are as follows. Although the high oxidation potential solvent had the advantages of high oxidation resistance and non-flammability, the high oxidation potential solvent had poor compatibility with the negative electrode and might have side reactions on the negative electrode. DTD might first form a stable interface protective film on the negative electrode, thereby suppressing side reactions of the high oxidation potential solvent on the negative electrode. In addition, DTD might generate lithium sulfate that structurally contained an alkoxy structure (—CH₂CH₂O—) during the process of film forming on the negative electrode. This could effectively adjust viscoelasticity of the interface protective film on the negative electrode, further improve kinetics of lithium ion transfer at the interface, and finally form a thin and dense interface protective film with good kinetics of lithium ion transfer on the negative electrode. In addition, DTD might also form a stable interface protective film on a surface of the positive electrode to further improve oxidation resistance of the nonaqueous electrolyte. Therefore, the addition of DTD can better improve cycle performance and kinetic performance of the lithium-ion battery, and might also improve high-temperature storage performance and hot box safety performance of the lithium-ion batteries to some extent.

Furthermore, when the nonaqueous electrolyte contained both DTD and FEC in the above film forming additives, the performance of the lithium-ion batteries, especially the cycle performance, was further improved. A possible reason is that: FEC might be reduced on the negative electrode to form a stable interface protective film, thereby weakening reduction reactions of DTD on the negative electrode. This might help to further improve film forming quality of DTD on a surface of the positive electrode, which further facilitated improvement of cycle performance of the lithium-ion batteries.

It may be seen from the test results of Example 4 and Examples 25 and 26 that after use of the mixed lithium salt formed by LiPF6 and LiFSI, the kinetic performance and hot box safety performance of the lithium-ion battery was further improved. A possible reason is that with advantages of moderate viscosity and a high degree of dissociation, LiFSI could promote ion conduction to improve electrical conductivity of the nonaqueous electrolyte, helping to obtain a lithium-ion battery with good kinetic performance. In addition, as thermal stability of LiFSI was higher, LiFSI also improved the hot box safety performance of the lithium-ion battery to some extent.

According to the disclosure and teaching of this specification, a person skilled in the art of this application may further make appropriate changes or modifications to the foregoing implementations. Therefore, this application is not limited to the foregoing disclosure and the described specific implementations, and some changes or modifications to this application shall also fall within the protection scope of the claims of this application. In addition, although some specific terms are used in this specification, these terms are used only for ease of description, and do not constitute any limitation on this application. 

What is claimed is:
 1. A nonaqueous electrolyte, comprising a nonaqueous solvent and a lithium salt, wherein the nonaqueous solvent comprises a carbonate solvent and a high oxidation potential solvent, wherein the high oxidation potential solvent is selected from one or more of compounds represented by formula I and formula II;

in formula I, R₁ and R₂ are independently selected from unsubstituted, partially halogenated or fully halogenated alkyl groups having 1 to 5 carbon atoms, and at least one of R₁ and R₂ is a partially halogenated or fully halogenated alkyl group having 1 to 5 carbon atoms; in formula II, R₃ is selected from partially halogenated or fully halogenated alkylidene groups having 1 to 6 carbon atoms; and based on a total weight of the nonaqueous solvent, a weight percentage of the high oxidation potential solvent is 10% to 60%, and further, 20% to 40%, wherein a halogen atom is selected from one or more of F, Cl, Br, and I, and further, the halogen atom is F.
 2. The nonaqueous electrolyte according to claim 1, wherein in formula I, R₁ and R₂ are independently selected from unsubstituted, partially fluorinated or fully fluorinated alkyl groups having 1 to 5 carbon atoms, and at least one of R₁ and R₂ is a partially fluorinated or fully fluorinated alkyl group having 1 to 5 carbon atoms, and further, R₁ and R₂ are independently selected from —CH₃, —CF₃, —CH₂CH₃, —CF₂CH₃, —CH₂CF₃, —CF₂CF₃, —CH₂CH₂CH₃, —CF₂CH₂CH₃, —CH₂CH₂CF₃, —CH₂CF₂CF₃, —CF₂CH₂CF₃, —CF₂CF₂CH₃, and —CF₂CF₂CF₃, and at least one of R₁ and R₂ is —CF₃, —CF₂CH₃, —CH₂CF₃, —CF₂CF₃, —CF₂CH₂CH₃, —CH₂CH₂CF₃, —CH₂CF₂CF₃, —CF₂CH₂CF₃, —CF₂CF₂CH₃, or —CF₂CF₂CF₃; and in formula II, R₃ is selected from partially fluorinated or fully fluorinated alkylidene groups having 1 to 6 carbon atoms, and further, R₃ is selected from —CHFCH₂CH₂CH₂—, —CF₂CH₂CH₂CH₂—, —CF₂CH₂CH₂CHF—, —CF₂CH₂CH₂CF₂—, —CH₂CH₂CHFCH₂—, —CH₂CHFCHFCH₂—, —CH₂CH₂CH(CF₃)CH₂—, —CF₂CH₂CH₂CH₂CH₂—, —CF₂CH₂CH₂CH₂CF₂—, —CH₂CH₂CH₂CHFCH₂—, —CH₂CHFCH₂CHFCH₂—, —CH₂CHFCH₂CHFCHF—, —CH₂CH₂CH₂CH₂CHF—, —CH₂CH₂CH₂CH(CF₃)CH₂—, —CF₂CH₂CH₂CH₂CH₂CH₂—, —CH₂CH₂CH₂CH₂CHFCH₂—, —CH₂CHFCH₂CH₂CHFCH₂—, —CF₂CH₂CH₂CH₂CH₂CF₂—, —CH₂CH₂CH(CH₃)CH₂CHFCH₂—, and —CH₂CH₂CH(CF₃)CH₂CHFCH₂—.
 3. The nonaqueous electrolyte according to claim 2, wherein the high oxidation potential solvent is selected from one or more of the following compounds:


4. The nonaqueous electrolyte according to claim 1, wherein the carbonate solvent is selected from one or more of cyclic carbonate and linear carbonate; the cyclic carbonate is selected from one or more of ethylene carbonate and propylene carbonate, and the linear carbonate is selected from one or more of ethyl methyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, methyl butyl carbonate, ethylene propyl carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate and dibutyl carbonate; and a weight ratio of the linear carbonate to the cyclic carbonate is 80:1 to 1:1, and further, 15:1 to 3:1.
 5. The nonaqueous electrolyte according to claim 4, wherein the carbonate solvent comprises at least one of ethyl methyl carbonate, dimethyl carbonate, and diethyl carbonate.
 6. The nonaqueous electrolyte according to claim 1, wherein room-temperature electrical conductivity of the nonaqueous electrolyte is greater than or equal to 5.0 mS/cm.
 7. The nonaqueous electrolyte according to claim 1, wherein the nonaqueous electrolyte further comprises a film-forming additive; the film-forming additive is selected from one or more of a cyclic carbonate compound with an unsaturated bond, a halogen-substituted cyclic carbonate compound, a sulfate compound, a sulfite compound, a sultone compound, a disulfonate compound, a nitrile compound, an aromatic compound, an isocyanate compound, a phosphazene compound, a cyclic anhydride compound, a phosphite compound, a phosphate compound, a borate compound, and a carboxylate compound; and the film-forming additive is further selected from one or more of 1,3-propane sultone, ethylene sulfate, fluoroethylene carbonate, difluoroethylene carbonate, vinylene carbonate, 1,3-propene sultone, adiponitrile, and succinonitrile.
 8. The nonaqueous electrolyte according to claim 7, wherein the film-forming additive comprises at least ethylene sulfate; and further, the film-forming additive comprises at least both ethylene sulfate and fluoroethylene carbonate.
 9. A lithium-ion battery, comprising a positive electrode plate, a negative electrode plate, a separator, and the nonaqueous electrolyte according to claim
 1. 10. The lithium-ion battery according to claim 9, wherein the positive electrode plate comprises one or more of Li_(1+x)Ni_(a)Co_(b)M′_((1−a−b))O_(2−c)Y_(c), and Li_(1+y)Ni_(m)Mn_(n)M″_(2−m−n)O_(4−p)Z_(p), wherein −0.1≤x≤0.2, 0.6≤a≤1, 0≤b<1, 0≤(1-a-b)<1, 0≤c<1, M′ is selected from one or more of Mn, Al, Mg, Zn, Ga, Ba, Fe, Cr, Sn, V, Sc, Ti, and Zr, and Y is selected from one or more of F, Cl, and Br; and −0.1≤y≤0.2, 0.4≤m≤1.2, 0.8≤n≤1.6, 0≤(2-m-n)≤0.3, 0≤p≤1, M″ is selected from one or more of Al, Mg, Zn, Ga, Ba, Fe, Cr, Sn, V, Sc, Ti, and Zr, and Y is selected from one or more of F, Cl, and Br.
 11. The lithium-ion battery according to claim 9, wherein the carbonate solvent is selected from one or more of cyclic carbonate and linear carbonate; the cyclic carbonate is selected from one or more of ethylene carbonate and propylene carbonate, and the linear carbonate is selected from one or more of ethyl methyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, methyl butyl carbonate, ethylene propyl carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate and dibutyl carbonate; and a weight ratio of the linear carbonate to the cyclic carbonate is 80:1 to 1:1, and further, 15:1 to 3:1.
 12. The lithium-ion battery according to claim 11, wherein the carbonate solvent comprises at least one of ethyl methyl carbonate, dimethyl carbonate, and diethyl carbonate.
 13. The lithium-ion battery according to claim 9, wherein room-temperature electrical conductivity of the nonaqueous electrolyte is greater than or equal to 5.0 mS/cm.
 14. The lithium-ion battery according to claim 9, wherein the nonaqueous electrolyte further comprises a film-forming additive; the film-forming additive is selected from one or more of a cyclic carbonate compound with an unsaturated bond, a halogen-substituted cyclic carbonate compound, a sulfate compound, a sulfite compound, a sultone compound, a disulfonate compound, a nitrile compound, an aromatic compound, an isocyanate compound, a phosphazene compound, a cyclic anhydride compound, a phosphite compound, a phosphate compound, a borate compound, and a carboxylate compound; and the film-forming additive is further selected from one or more of 1,3-propane sultone, ethylene sulfate, fluoroethylene carbonate, difluoroethylene carbonate, vinylene carbonate, 1,3-propene sultone, adiponitrile, and succinonitrile.
 15. The lithium-ion battery according to claim 14, wherein the film-forming additive comprises at least ethylene sulfate; and the film-forming additive further comprises at least both ethylene sulfate and fluoroethylene carbonate.
 16. The lithium-ion battery according to claim 9, wherein in formula I, R₁ and R₂ are independently selected from unsubstituted, partially fluorinated or fully fluorinated alkyl groups having 1 to 5 carbon atoms, and at least one of R₁ and R₂ is a partially fluorinated or fully fluorinated alkyl group having 1 to 5 carbon atoms, and R₁ and R₂ are independently selected from —CH₃, —CF₃, —CH₂CH₃, —CF₂CH₃, —CH₂CF₃, —CF₂CF₃, —CH₂CH₂CH₃, —CF₂CH₂CH₃, —CH₂CH₂CF₃, —CH₂CF₂CF₃, —CF₂CH₂CF₃, —CF₂CF₂CH₃, and —CF₂CF₂CF₃, and at least one of R₁ and R₂ is —CF₃, —CF₂CH₃, —CH₂CF₃, —CF₂CF₃, —CF₂CH₂CH₃, —CH₂CH₂CF₃, —CH₂CF₂CF₃, —CF₂CH₂CF₃, —CF₂CF₂CH₃, or —CF₂CF₂CF₃; and in formula II, R₃ is selected from partially fluorinated or fully fluorinated alkylidene groups having 1 to 6 carbon atoms, and R₃ is selected from —CHFCH₂CH₂CH₂—, —CF₂CH₂CH₂CH₂—, —CF₂CH₂CH₂CHF—, —CF₂CH₂CH₂CF₂—, —CH₂CH₂CHFCH₂—, —CH₂CHFCHFCH₂—, —CH₂CH₂CH(CF₃)CH₂—, —CF₂CH₂CH₂CH₂CH₂—, —CF₂CH₂CH₂CH₂CF₂—, —CH₂CH₂CH₂CHFCH₂—, —CH₂CHFCH₂CHFCH₂—, —CH₂CHFCH₂CHFCHF—, —CH₂CH₂CH₂CH₂CHF—, —CH₂CH₂CH₂CH(CF₃)CH₂—, —CF₂CH₂CH₂CH₂CH₂CH₂—, —CH₂CH₂CH₂CH₂CHFCH₂—, —CH₂CHFCH₂CH₂CHFCH₂—, —CF₂CH₂CH₂CH₂CH₂CF₂—, CH₂CH₂CH(CH₃)CH₂CHFCH₂—, and —CH₂CH₂CH(CF₃)CH₂CHFCH₂—.
 17. A battery module, comprising the lithium-ion battery according to claim
 9. 18. A battery pack, comprising the battery module according to claim
 17. 19. An apparatus, comprising the lithium-ion battery according to claim 9, wherein the lithium-ion battery is used as a power source for the apparatus.
 20. The apparatus according to claim 19, wherein the apparatus is one selected from the group consisting of a battery electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, an electric vessel, and an energy storage system. 